A collegue suggested that I put the parasitics of the kapacitor in discrete components in series, and that fixed the problem. Bug?
/Johan
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--- In LTspice@..., Christian Thomas <ct.waveform@...> wrote:
I used to get strange differences between linear and log scales in earlier
version of LTspice, though I haven't had any in the last year or two. They
were never explained, but they certainly disappeared.
If it's not an early version, have a look at the no of points per octave you
are using. If you have too few there can be some very strange plotting as
the otherwise seemingly excellent interpolation does its best with the
derivatives it's given. A bouncing ball shape is one definite symptom of
this.
CT
On 18 September 2011 20:15, gasoltroll <johan.lans@...> wrote:
**
Hi
i'm looking at an impedance curve of a non-ideal tantalum capacitor in
LTSpice. The test circuit and impedance curve is seen in this screengrab:
The spice file is here .
So, the imdpedance curve shows the expected impedance minimum, but also an
unexpected maximum at about 100MHz, where there is also a polarity switch in
phase. This feature does not show up if I do an impedance plot in octave:
octave:1> f = [1000:1000:1e9];
octave:2> C = 2e-3C = 0.0020000
octave:3> R = 2e-3R = 0.0020000
octave:4> L = 1e-9L = 1.0000e-09
octave:5> z = R + f.*2*pi*j*L-1./(f.*2*pi*j*C)
octave:6> loglog(f,abs(z))
octave:7> semilogx(f,atand(imag(z)./real(z)))
Which result in these plots
The parameters in the octave code are the same as in LTSpice component.
Anyone know where this comes from? The phases look pretty different, is
there something wrong with the test circuit?
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